The present invention relates generally to metal roof structures for use in buildings. More particularly, the present invention concerns uniformly insulated metal roof structures.
Metal roof for use in connection with various building structures have, of course, been known for many years. Since metal is a notoriously good conductor of heat, such roofs have been thermally inefficient and the need for insulating metal roofs has long been known. Moreover, the need to insulate a metal roof is readily apparent to any occupant during the temperature extremes of summer and winter since the buildings are hard to heat in the winter and hard to cool in the summer without some type of roof insulation.
While there are many ways of insulating roof structures, one commonly employed method uses rigid or semi-rigid foamed insulation materials. A second commonly employed technique uses roll insulating material. When roll insulated material is employed, retardation of heat flow through the roof is obtained by the expanded thickness of the roll which results when it is unrolled.
A conventional metal roof construction requires placement of this roll insulation over horizontal supports or purlins with roofing panels being placed on top of the insulation and subsequently attached to the purlins. The attachment of the roof panels to the purlins creates an area where the roll insulation is compressed from its expanded thickness to a considerably smaller thickness. Typically, this compressed thickness may be in the neighborhood of one to two tenths of an inch. Since the desirable heat retardation properties are a function of the actual thickness of the insulating material, the compressed areas above the purlins are, in effect, regions where increased heat flow or heat loss occurs.
In recent years there has been a considerable emphasis on increasing the energy efficiency of buildings of all types. This emphasis is, in at least part, due to the substantially increased costs of heating and cooling buildings. The regions of increased heat flow created by the compressed roll insulation above the purlin has been a source of concern in terms of increasing the thermal efficiency of metal roof structures.
One typical metal roof construction uses roof panel mounting clips positioned above insulating material and directly attached to the purlins in order to secure roof panels to the roof structure. See, for example, U.S. Pat. No. 4,213,282, issued July 22, 1980 to Heckelsberg. Since the roof panel attachment clips are located at spaced intervals along the purlins, elongated thermal blocks are laid along the run of each purling between adjacent roof panel supporting clips. Typically, these thermal blocks have a width approximately coextensive with the width of the purlin surface and are fashioned from materials such as urethane foam or expanded styrene.
While this assembly constitutes a considerable improvement in the thermal efficiency of a roof structure, heat losses still occur in the vicinity of the roof panel mounting clips due to the compressed insulation between the roof panel mounting clip and the underlying purlin. In addition, compression of the roll insulation beneath the thermal block has a tendency to cause the thermal block to bend upwardly so that its center portion is at a higher elevation than its end portions. This distortion of the thermal block causes an effect known as "pillowing" in the overlying roof panels and becomes a significant problem when roll insulation is used in thicknesses exceeding four inches. Pillowing not only adversely affects appearance of the roof but also makes the roof panels more difficult to place and to fasten in the roof panel structure. Another deficiency of this roof structure concerns thermal block dislocations. Since the roof panels expand and contract in response to ambient temperature variations, the panel movement may cause the thermal block to be dislocated from its overlying relationship with the purlin. In this event, the additional insulating value of the thermal blocks can be lost or substantially diminished.
Another problem in construction of insulated metal roof assemblies concerns the difficulty of placing roof panel attachment clips above the insulation. These clips must not only be properly spaced but also must be attached to the purlin in a secure manenr. In the past, spacing between clips was usually measured. As a result, it was a cumbersome and time consuming procedure to mount the clips to the purlins on top the roll insulation. Moreover, the problem of clip attachment is compounded as the thickness of the roll insulation increases causing the roof panels to distort due to the upward pressures of the insulation.
In one attempt to compensate for the problem of insulation compression above a purlin, it has been proposed to employ generally U-shaped brackets, placed over the purlins to support insulating materials between adjacent purlins. A strip of insulating material is then placed above the bracket. Roof panels are attached to the purlin by fasteners which pass directly through the insulating strip and into the purlin. See, for example, U.S. Pat. No. 4,346,543, issued Aug. 31, 1982 to Wilson et al; and U.S. Pat. No. 3,662,509 issued May 16, 1972 to Studzinski.
In an insulated metal wall structure having surfaces of corrugated metal and batts of insulation positioned therebetween, it has also been proposed to employ a spacer block of foamed insulating material such as polyurethane. The spacer block is provided with one or two metal facing plates for the purpose of spacing the walls from one another. One end of the space block may have a pair of leg portions each of which engages convolutions of an adjacent wall such that a crest of the wall is received by a groove between the legs. See, for example, U.S. Pat. No. 3,474,583 issued Oct. 28, 1969 to Manias.
A heat insulating structural member is also known in which a heat insulating core having a height substantially exceeding its width is provided with a pair of U-shaped caps made of metal like aluminum are provided on the top and bottom edges of the insulating material core to complete the structural member. Other patents of more general interest are U.S. Pat. No. 3,373,534 issued Mar. 19, 1968 to Berridge and U.S. Pat. No. 3,879,911 issued Apr. 29, 1975 to Howells.
The various prior art devices do not show a solution to the problems of the thermal short circuit resulting from compression of the roll insulation, the movement of a thermal block caused by improper placement or thermal expansions and contractions and pillowing resulting from forces exerted by the compressed insulation material. Moreover, there is not teaching of a method of attaching the roof support clips to their proper predetermined positions along purlins.